Recently, with spread of a digital technology in electronic devices such as an acoustic device and a video device, there is a strong demand to improve performance of a speaker used in the electronic devices. Particularly, in components constituting the speaker, performance of a diaphragm largely affect a determination of sound quality, and there is a need for development of a high-performance diaphragm implementing the better sound quality. A method of producing conventional speaker diaphragm will be described with reference to the drawing. FIG. 10 is a sectional view illustrating a conventional resin speaker diaphragm, which is formed by injection molding. Diaphragm 7 is produced such that a pellet of a resin such as polypropylene is thermally dissolved and injected in a mold in which a shape setting is previously performed. Generally a single material such as polypropylene is used as a kind of the resin material used in the injection molding. Additionally, in order to adjust a physical property of the diaphragm, namely, a characteristic and sound quality of the speaker, sometimes different kinds of resins are mixed and used as the material for diaphragm 7.
As to the physical property that is hardly adjusted only by the resin, the physical property is adjusted by mixing a reinforcing material such as mica, thereby adjusting the characteristic and sound quality of the speaker. A pulp material is mixed in order to increase a degree of freedom of the physical property adjustment, thereby adjusting the sound quality. In the diaphragm in which the resin and the pulp material are mixed, the degree of freedom of the sound quality adjustment is increased, and moisture-resistant reliability can be ensured. However, there is the demand to improve the sound quality.
For example, PTL 1 and PTL 2 are known as a technology related to the subject application.